Histochemical and ultrastructural characterization of primary cardiac chondrosarcoma

A cardiac chondrosarcoma was found in the right atrium of a Golden Retriever dog. Macroscopically, the right atrial lumen was filled with a 6- X 12- X 8-mm white glossy mass, which was diffusely attached to the underling myocardium. The mass was composed of spindle-shaped mesenchymal neoplastic cells loosely packed in light basophilic matrix, with focal areas of tightly packed cells in linear formation similar to the pattern of a growth plate. Tumor cells were positive when stained for vimentin and neuron-specific enolase, and weakly positive for S-100 protein. Ultrastructurally, neoplastic cells had abundant, dilated rough endoplasmic reticulum, Golgi apparatus, bundles of intermediate fibers, and primitive intercellular junctions between adjacent tumor cells. Based on morphologic, ultrastructural, histochemical, and immunohistochemical characteristics, this tumor was diagnosed as a chondrosarcoma.